1. Technical Field
The present invention relates to a sheet basis weight sensing device and method for sheets of paper, and to an image forming apparatus including the sheet basis weight sensing device.
2. Related Art
Conventionally, various items have been used for evaluating printing characteristics of a sheet of paper or recording medium (to be referred to as a sheet, hereinafter) on which an image is formed, such as thickness, density, basis weight, smoothness, and air permeability. Many items representing properties and qualities of the sheet are listed in Paper, Board and Pulp—Vocabulary of the Japanese Industrial Standard (JIS P0001), including the basis weight, which represents the weight of the paper per square meter [g/m2]. The basis weight is represented by the density of the sheet multiplied by the thickness (that is, basis weight=density*thickness).
Image forming apparatuses can be configured to incorporate a sensing device capable of identifying the thickness and type of various sheets reliably and accurately during conveyance of the recording medium through the apparatus during image formation. However, since identifying only the thickness or the type of the sheet alone does not provide the sheet density, the basis weight cannot be accurately identified.